There is considerable medical interest in secreted and membrane-associated mammalian proteins. Many such proteins, for example, cytokines, are important for inducing the growth or differentiation of cells with which they interact or for triggering one or more specific cellular responses.
The demonstrated clinical utility of several secreted proteins in the treatment of human disease, for example, erythropoietin, granulocyte-macrophage colony stimulating factor (GM-CSF), human growth hormone, and various interleukins, illustrates the importance of secreted proteins.
Many membrane-associated proteins are receptors which bind a ligand(s) and transmit an intracellular signal. As such, membrane-associated proteins can be used to identify (or design) small molecules which act as agonists or antagonists of the ligand.